If your book is part of the Search Inside feature on Amazon.com, you might be able to get some incredible statistics about your book, including its reading level, word count, average words per sentence, % of complex words, and words per dollar (based on the retail price of your book).
If you'd like to read an interesting post comparing books by Malcolm Gladwell, Seth Godin, and a few other authors, go here: http://www.stevenberlinjohnson.com/2007/10/ this-may-be-old.html?cid=87592892#comment-87592892.
Perhaps the most interesting feature of the above post is how books with fewer average words per sentence and a smaller % of complex words sell better. In other words, if you write shorter sentences and use less complex words, you have a greater chance of becoming a bestselling author. Interesting.